This invention relates to the selective gas phase ethylation of xylene to form a highly isomerically-pure dimethylethylbenzene product and to the use of catalyst compositions comprising metal-modified, crystalline borosilicate molecular sieves, incorporated into an inorganic matrix, for carrying out such selective ethylation. More particularly, this invention relates to the selective gas phase conversion of xylene to highly isomerically pure 3,4-dimethylethylbenzene by contacting xylene, pure or in a mixture, with an ethylating agent under hydrocarbon conversion conditions in the presence of a catalyst composition comprising a metal-ion-modified, crystalline borosilicate molecular sieve incorporated in an inorganic matrix in which the metal ion is intimately associated with the silica framework lattice. The process offers a simple route from xylene to a highly isomerically-pure 3,4-dimethylethylbenzene product having reduced isomer purification problems.
Catalyst compositions, generally useful for hydrocarbon conversion, based upon AMS-1B crystalline borosilicate molecular sieves have been described in U.S. Pat. Nos. 4,268,420, 4,269,813, 4,285,919, and published European Application No. 68796, all of which are incorporated herein by reference.
In U.K. Pat. No. 2,024,790B, catalyst compositions containing high specific surface area crystalline silica based materials modified by boron, which have been impregnated by Pt, Pd, Ni, Co, W, Cu, and Zn, are taught, which materials have catalytic usefulness in, inter alia, the alkylation of toluene with methanol. European Pat. No. 38682 teaches methanol-to-synthesis-gas conversion catalysts comprising a crystalline silica modified by inclusion of cobalt in the crystal lattice in place of a proportion of the silicon atoms. The catalyst is prepared by mixing in water or alcohol a source of silicon, a source of cobalt, a nitrogenous base such as a quaternary ammonium compound and, optionally, a mineralizing agent, and/or an inorganic base like sodium hydroxide. Also, European Pat. No. 63436 describes a methanol or olefin conversion catalyst of general formula 0-9 M.sub.2 O:aY.sub.2 O.sub.3 :at least 100XO.sub.2 :0-35H.sub.2 O, where M is a monovalent cation or 1/n of a cation of valency n, a is from 0-9, X is silicon and Y can be one or more of aluminum, iron, chromium, vanadium, molybdenum, arsenic, antimony, manganese, gallium, or boron.
Selective production of 3,4-dimethylethylbenzene by alkylation of xylene over zeolite catalysts having a silica-to-alumina ratio of at least about 12 and a Constraint Index of greater than 2 and up to about 12 is taught in European Patent Application No. 0021600. The class of zeolites is exemplified by ZSM-5, ZSM-11, ZSM-23, and ZSM-35.
Catalyst compositions made using crystalline borosilicate molecular sieves have shown a great utility for hydrocarbon conversion reactions such as aromatic isomerization and alkylation reactions. While excellent for many purposes, it is desirable to fine-tune the borosilicate family of catalysts to perform more selectively in a particular type of hydrocarbon conversion reaction. Now it has been found that by incorporating a small amount of metal ion in the formation of a HAMS-1B molecular sieve, crystalline borosilicate-based molecular sieves, metalloborosilicates, can be produced which are very selective for producing the 3,4-dimethylethylbenzene isomer during the gas phase ethylation of a xylene alone or in a mixture.